Effect of blending calcium compounds on hydrolytic degradation of poly( -lactic acid-co-glycolic acid)

To clarify the effect of blending calcium compounds with different acidity or basicity on the degradation of poly( -lactic acid-co-glycolic acid) (PLGA), composite materials composed of PLGA incorporated with 30 mass% of calcium dihydrogenphosphate (CDHP), calcium hydrogenphosphate, calcium phosphate, and calcium carbonate (CC) were prepared by mixing in dioxane followed by freeze-drying. The porous composite materials were then compressed to yield nonporous films with 0.5 mm thickness. The blend films and the unfilled films as a control were immersed in phosphate-buffered saline (pH 7.4) at 37°C. Specimens were removed at 1, 2, 3, 4, 6, and 8 weeks and subjected to measuring of water absorption, mass loss, thickness change, and molecular weight. The temporal changes in appearance and measurements for the five materials differed from each other; especially, the CC blend differed from the other four materials. The degradation of PLGA decreased with increasing basicity of the calcium compounds blended. The most basic CC was most effective to delay the degradation, while the most acidic CDHP was least effective. However, even CDHP had appreciable degradation-delaying effects compared with unfilled PLGA. Thus, the findings of the present study suggest that degradation of PLGA can be varied by blending inorganic compounds with different basicity.